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More evidence monkeypox spreads before symptoms appear

According to an observational study, there may be substantial monkeypox transmission prior to the onset of symptoms, making timely isolation of infected individuals more difficult.

Analysis of contact tracing data from the UK Health Security Agency (UKHSA) shows that transmission can be detected up to 4 days before symptom onset, and that 53% of transmission occurs during this pre-symptomatic phase, Thomas Ward of the UK Health Security Agency reports London and colleagues.

“It takes 16 to 23 days of quarantine to detect 95% of potentially infected people,” they said in BMJ.

After right truncation and adjustment for epidemic stage bias, the research team found that the average incubation period was estimated to be 7.8 days, while the average serial interval (from the onset of symptoms in the main case patient to the appearance of secondary contacts Symptom time) was 9.5 days.

“The median serial interval of es is shorter than the incubation period, suggesting much more presymptomatic transmission than previously thought and confirmed by analysis of individual-level data,” Ward and co-authors wrote.

Findings modeling studies suggest that many infections cannot be prevented by requiring individuals to isolate after noticing symptoms and that “presymptomatic transmission … will have important implications for global infection control,” says Esther Freeman, MD. Massachusetts General Hospital in Boston and colleagues note in an accompanying editorial.

Freeman’s group noted that post-exposure vaccination of contacts detected by symptomatic individuals alone may not be sufficient, so the UK and US The shift from prevention to pre-exposure prophylaxis that includes some high-risk populations” is on the right track. Between May 2022 and August 2022, 2,746 people in the UK had an incubation period, which is the time from exposure to symptoms. The time to case doubling was 9.07 days (95% CI 7.08-12.63) on 6 May, when the first UK monkeypox case was reported, and 29 days (95% CI 23.44-38.02).

Participants were all infected with PCR-confirmed monkeypox virus, had a mean age of 38 years, and 95% reported being gay, bisexual or MSM.

Researchers found that 10 of 13 linked patients had documented pre-symptomatic transmission.

Respondents in case questionnaire (mean age, 37 years), “53 percent had a history of an STI in the past year, and 31 percent had at least 10 or more sexual partners in the past three months,” Ward and his colleagues said. This is in stark contrast to “the Democratic Republic of the Congo, where the median age was 10 years in 2016 and only 42% of cases were older than 5 years in 2020. This suggests a change in the main route of transmission of monkeypox virus. Epidemic in 2022 disease.”

Regarding their finding that 53% of transmission occurred in the presymptomatic phase, the authors caution, “Since the serial interval depends on the incubation period, this finding is a Limitations of other studies include the use of “contact tracing to identify correct case-contact pairs and self-reported date of symptom onset,” they noted in a press release. They also caution that the data may not necessarily be directly applicable to other populations with different transmission patterns.

Freeman’s group emphasizes that lack of equitable access to vaccines to control monkeypox is a serious problem and becomes even more problematic if presymptomatic transmission occurs. “In the United States… blacks accounted for 50 percent of monkeypox infections but received only 12 percent of the vaccines,” they wrote.

“From a health system perspective, vaccination is likely to be more cost-effective than managing the consequences of preventable infection, including hospital admissions, loss of income during isolation, and long-term complications,” they said.

Freeman and colleagues also stress that monkeypox outbreaks in Europe and North America may be on the wane, but “we have a responsibility to deploy effective virus control tools globally—not just In wealthy countries. These tools include studies to understand transmission dynamics in African settings and inclusion of endemic countries in vaccine trials.”

  • Kate Kneisel of Belleville, Ontario Freelance medical reporter.


    Ward and co-authors disclose no industry affiliation.

    Freeman and coauthors disclosed their relationship with the World Health Organization monkeypox guideline development group.



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